Mystery stalling issue on 7.4 mercruiser

[alldodge]

No power at the purple wire,

This is the problem if the key is in the run or ON position

 

[BomoBoater]

I found no power at S when turning the key to start
Which switch might be bad? neutral safety switch or the ignition switch?

 

[alldodge]

I found no power at S when turning the key to start
Which switch might be bad? neutral safety switch or the ignition switch?

Power comes in on the Red/Purple wire (your B terminal) the key switch transfers power to the Purple wire when the key is turned ON, and to start (S terminal) when cranking. Neither the neutral safety nor kill switch have anything to do with power going to the purple wire AT THE SWITCH. Once power leaves the switch, then the neutral safety switch and kill switch are in the circuits.

Power leaves the switch at the purple wire and then goes to the kill switch, then goes to ignition circuits which all are also purple wires

Power leaves the S terminal when turned to start, thru the neutral safety switch to the solenoid

 

[BomoBoater]

I tried again today

Kill switch is bypassed.

I used a different switch switch that I know works. Nothing.
In run or start at the key there is no power at the s or I wire.
I connected the B&I wires directly and jumpered the S wire, (Hotwire) Nothing.
I removed grey wire at coil, nothing.
There is 12.6v at the B wire at the helm.

I bypassed the helm, and made the connections between coil&slave solenoid, jumpered thevother terminal, and she fired right up. I only let it run a minute.

So I know the engine works.

Where re should I be looking to figure out why both the purple I wire and red yellow S wire don't work?

 

[alldodge]

In that case you probably have a bad connection. Your meter sees 12V on the B wire, but I'm guessing as soon as you turn the key or connect the wires together your voltage drops to zero. If this is the case, then you need to trace the red/puple wire back to the battery.

Connect meter to B terminal and turn key ON, see if 12V are found
if NO
Connect meter to starter post and turn key to ON, see if it stays at 12V
If good
Connect meter to the 50 amp breaker with key ON, check both terminals
If good
Pull 10 pin engine connector and see if 12V is found on any of the engine side pins

Now if the Key is ON and you do get 12V on the purple wire, let us know

 

[BomoBoater]

Testing more as we speak

 

[BomoBoater]

Key off at b terminal 12+v
.07 at I, 0 at s

Key on at I .005v.
at s 0v
at b all over the place but less than 1v

At starter terminal start 12+v
Both terminals at 50amp fuse 12+ volts
Checking for Voltage shows .393v from Engine side of harness at one point.
Purple wire beeps loudly @2 connections from dash to harness plug and quietly at a large connection w/ohm. Only beeps at 1 with test light.
Red/yellow beeps at one plug with both.

 

[alldodge]

The red/purple wire comes thru at pin 6 and it should be there even when connector is disconnected. If not there, then there is corrosion somewhere, and can also be inside the main connector

 

[BomoBoater]

I had continuity only here with test light

 

[BomoBoater]

But when using a jumper wire I found it also here

 

[BomoBoater]

This is the one spot with voltage

 

[alldodge]

But when using a jumper wire I found it also here

That is the helm side, need the engine side

 

[alldodge]

This is the one spot with voltage

That is pin 10 and the correct side, so your not getting power on pin 6, then there is a disconnect or corrosion

 

[BomoBoater]

Would you recommend I open up the receiving end of the plug and examine the inner connections first?

 

[alldodge]

Measure resistance between the 50 amp breaker to pin 6 (its probably high or erratic). If this is the case, then there is no easy way to fix I'm aware of. You could get into the connector but there not designed to be repaired (maybe someone has an idea)

I would get another connector and replace the one you have, like this
https://www.michiganmotorz.com/cust...nbEmJ5LPTWWVeRA8euZdCbWYY_tWH1zWKkBoCjYDw_wcB

Can try to cut into the back of it and see if it can be repaired. The pin might be able to be pushed/pulled out then reinstalled, but my guess is will need something to help get the two pins together, and not be pushed out when the other connector is installed

 

[alldodge]

Could also find about any old Merc engine side harness and cut the end off and splice on yours

Or cut the same pin from both connectors and splice in new wire to make the connection, would be cheapest way to go

 

[BomoBoater]

Good news, bad news today.
I Decided to clean both male and female parts of the harness pins, (although my mechanic told me he did it). After some 400grit lo and behold I had voltage at pin #6. 12+v, and the same .396v at pin 10.
Still no joy at the helm.

Good thing I did that before splicing in a new harness.

So... where do I go next. I have to run into the issue eventually right?

 

[BomoBoater]

So now this is what I get at the ignition

Key off
12+v at B
.035v at S
0v at I

Key "run"
Fluctuating voltage at B. .035v-.4v
.005v at S
.013v at I

Key "start"
Same fluctuating voltage at B
.008v at I
Fluctuating voltage at S .03-.4v

still no instruments, still no cranking

 

[BomoBoater]

Problem solved today.

Digital meter gave voltage on the red wire to the B terminal. So I ASSUMED it was good. I put a test light on it today, and no light. A-ha. Voltage, but not enough current.
I ran a jumper wire directly to the battery from the B terminal. The instruments came on and she fired right up.
I spliced a new 10ga wire about halfway into the harness and hooked it up to the 20amp ignition fuse where the old wire was.

I ran her over an hour today without a hiccup.

What is it they say about assuming...

thanks everyone

 

[Ed Harris]

Now that is some electrical troubleshooting right there. Good job on staying with this "little" project. It is like it became a quest that needed to be conquered.